Compact modeling pertains to the development of models for integrated semiconductor devices for use in circuit simulations. The models are used to reproduce device terminal behaviors with accuracy, computational efficiency, and relative model simplicity for a circuit or system-level simulation, for future technology nodes. The users of the models are typically the IC designers. The industry's dependence on accurate and time-efficient compact models continues to grow as circuit operating frequencies increase and device tolerances scale down with associated increases in chip device count, and analog content in mixed-signal circuits. Compact modeling is an important step in the design cycle of modern IC products. More specifically, it is an important step for information transfer from technology development and fabrication to circuit and product design.
Circuit simulations are used in integrated circuit design to predict how a circuit behaves prior to the circuit being physically implemented, e.g., fabricated. Circuit simulators, such as Simulation Program with Integrated Circuit Emphasis (SPICE), rely on mathematical compact models of circuit elements to perform such simulations. The compact models are typically expressed as a set of equations and a set of parameters for the equations that predict the current and charges at terminals of a semiconductor device as a function of the voltages at the terminals. The compact models are fit to characteristics of a particular process in which some of the characteristics are represented by sample devices and some of the characteristics are different from available hardware. Such compact models are typically built while the process is still under development, and historical information from previous generations is often used to inform the characteristics of the model of the new, and empirically untested, generation. Such methods of extrapolation have limitations, however, such as when there are major modifications in transistor architecture (such as from bulk planar to FinFET or nanowire), or materials (such as from silicon to InGaAs), or for widely disparate characteristics such as dielectric thickness, threshold voltage, and physical dimensions. Alternatively, and preferably, utilization of physics-based models to inform the parameters of the compact model can circumvent these issues.